Order $18$ has exactly five group types: two abelian and three nonabelian.Suggest a slogan
Up to isomorphism there are five groups of order \(18\). The abelian ones are \(\ZZ/18\ZZ\) and \((\ZZ/3\ZZ)^2\times\ZZ/2\ZZ\), and the nonabelian ones are
the dihedral group \(D_9\) of order \(18\),
\(S_3\times\ZZ/3\ZZ\),
the generalized dihedral group \((\ZZ/3\ZZ)^2\rtimes\ZZ/2\ZZ\), with the generator of \(\ZZ/2\ZZ\) acting by inversion.
What are the groups of order 18?